Many clinical conditions, deficiencies, and disease states may be remedied or alleviated by supplying to the patient a one or more biologically active factors produced by living cells or removing from the patient deleterious factors which are metabolized by living cells. In many cases, these factors may restore or compensate for the impairment or loss of organ or tissue function. Examples of disease or deficiency states whose etiologies include loss of secretory organ or tissue function include:
(a) diabetes, wherein the production of insulin by pancreatic islets of Langerhans is impaired or lost;
(b) hypoparathyroidism, wherein the loss of production of parathyroid hormone causes serum calcium levels to drop, resulting in severe muscular tetany;
(c) Parkinsonism, wherein dopamine production is diminished; and
(d) anemia, which is characterized by the loss of production of red blood cells secondary to a deficiency in erythropoietin. The impairment or loss of organ or tissue function may result in the loss of additional metabolic functions.
Accordingly, many investigators have attempted to reconstitute organ or tissue function by transplanting whole organs, organ tissue, or cells which provide secreted products or affect metabolic functions. Moreover, transplantation may provide dramatic benefits but is limited in its application by the relatively small number of organs suitable and available for grafting. In general, the patient must be immunosuppressed in order to avert immunological rejection of the transplant, which results in loss of transplant function and eventual necrosis of the transplanted tissue or cells. In many cases, the transplant must remain functional for a long period of time, even for the remainder of the patient's lifetime. It is both undesirable and expensive to maintain a patient in an immunosuppressed state for a substantial period of time.
A desirable alternative to such transplantation procedures is the implantation of cells or tissues within a physical barrier which will allow diffusion of nutrients, waste materials, and secreted products, but block the cellular and molecular effectors of immunological rejection. A variety of devices which protect tissues or cells producing a selected product from the immune system have been explored. These include extravascular diffusion chambers, intravascular diffusion chambers, intravascular ultrafiltration chambers, and implantation of microencapsulated cells. These devices would alleviate the need to maintain the patient in an immunosuppressed state. A problem with known devices is central necrosis of cells growing inside the devices. Central necrosis can occur after long-term implantation and give rise to widespread cell death inside the capsule.
A method and device for providing higher surface area per unit volume of the chamber for distributing cells and improved diffusion for delivering appropriate quantities of needed substances, such as growth factors, neuropeptides, enzymes, hormones, or other factors or, providing other needed metabolic functions, for an extended period of time would be very advantageous to those in need of long-term treatment.
Various types of cell capsules are known. For example, U.S. Pat. No. 5,786,216 discloses capsules with an inner support giving tensile strength to the device. The support may include fins extending radially along the axis of the capsule or the external surface of the inner support may be roughened or irregularly shaped. U.S. Pat. No. 6,627,422 discloses device with a mesh or yarn support for attachment of cells. WO 2006/122551 discloses an encapsulated cell device having an elongate tether comprising a stiffener to make the tether more rigid.